would , could

Could のほうが　丁寧・上品な　お願い　　で
Would は　丁寧なのですが、命令に近い　感じもあります。
would だと基本的に意思をきいてるので　手伝いたいですか？　どんだけ〜　感あり
友人同士なら　Would でもいいけど

原則的に　Could ...のほうが　上品で　おすすめです。


過去形にすることで　遠回し　上品になる　というのは　日本語も同じ　
いただけましたでしょうか

please refer to these sites. please once read these contents in these sites.
I suppose your question points would be solved by comprehending the content.
then re-post your unclear point to this site.

:Difference Between Could and Would.
https://pediaa.com/difference-between-could-and-would/
:"Could You" vs "Would You".
https://engoo.com/blog/2021/04/20/could-you-vs-would-you-whats-the-difference/